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Molecular Modeling of Polymers 16. Gaseous Diffusion in Polymers: A Quantitative Structure-Property Relationship (QSPR) Analysis (1997)

Patel, Hitesh C. ; Tokarski, John S. ; Hopfinger, A. J.

Springer

Pharmaceutical research 14 (1997), S. 1349-1354

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ISSN: 1573-904X

Keywords: diffusion ; polymers ; gases ; bulk modulus ; QSPR

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract Purpose. The purpose of this study was to identify the key physicochemical molecular properties of polymeric materials responsible for gaseous diffusion in the polymers. Methods. Quantitative structure-property relationships, QSPRs were constructed using a genetic algorithm on a training set of 16 polymers for which CO2, N2, O2 diffusion constants were measured. Nine physicochemical properties of each of the polymers were used in the trial basis set for QSPR model construction. The linear cross-correlation matrices were constructed and investigated for colinearity among the members of the training sets. Common water diffusion measures for a limited training set of six polymers was used to construct a 'semi-QSPR' model. Results. The bulk modulus of the polymer was overwhelmingly found to be the dominant physicochemical polymer property that governs CO2, N2 and O2 diffusion. Some secondary physicochemical properties controlling diffusion, including conformational entropy, were also identified as correlation descriptors. Very significant QSPR diffusion models were constructed for all three gases. Cohesive energy was identified as the main correlation physicochemical property with aqueous diffusion measures. Conclusions. The dominant role of polymer bulk modulus on gaseous diffusion makes it difficult to develop criteria for selective transport of gases through polymers. Moreover, high bulk moduli are predicted to be necessary for effective gas barrier materials. This property requirement may limit the processing and packaging features of the material. Aqueous diffusion in polymers may occur by a different mechanism than gaseous diffusion since bulk modulus does not correlate with aqueous diffusion, but rather cohesive energy of the polymer.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1012156318612

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Molecular modeling of polymers. 10. Characterization of conformational transitions of poly(acrylic acid) and poly(methacrylic acid) using dyad structures (1994)

Ravi, M. ; Hopfinger, A. J.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 1033-1047

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ISSN: 0887-6266

Keywords: molecular modeling ; poly(acrylic acid) ; poly(methacrylic acid) ; dyad structures ; conformational transitions ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: The conformational profiles of nearest side-chain neighbors, methylene-dyad structures, of poly(acrylic acid), PAA, and poly(methacrylic acid), PMA, were determined as a function of tacticity, extent of ionization, and presence of counterion. The dominant backbone conformer states are quite similar for both isotactic and syndiotactic diads in a common charge state. Thus, the overall dimensional properties of isotactic syndiotactic and atactic chains of PAA or PMA, based upon dyad interactions, are predicted to be alike for a given charge state. Significant deviations from precise t, g+, and g- states are found for the dyad minimum energy conformations. The rod-to-coil and coil-to-rod transitions observed in PAA and PMA, respectively, as a function of increasing counterion concentration can be explained, to a large extent, by the conformational profiles of the corresponding dyad model structures. © 1994 John Wiley & Sons, Inc.

Additional Material: 3 Ill.